This invention relates to a hot water circulating system, and more particularly to a hot water circulating system which is adapted to forcibly circulate hot water heated in a water boiler by means of a vapor pressure produced in the water boiler without using a circulating pump.
In a coffee syphon which has been widely used to make coffee, when water in a lower pot of the coffee syphon is boiled, a vapor pressure produced in the lower pot causes the water to be forcibly pushed up into an upper pot of the syphon, resulting in only vapor pressure being in the lower pot. When the syphon is decreased in temperature, vapor in the lower pot is liquefied to cause a negative pressure to be produced therein, so that the water forced up to the upper pot is caused to forcibly flow down to the lower pot by suction, during which coffee is made.
The above-described principle of the coffee syphon has been widely utilized in a conventional hot water circulating system, as disclosed in Japanese Patent Publication No. 33664/1976, Japanese Utility Model Publication No. 53929/1982, Japanese Utility Model Publication No. 2403/1987 and Japanese Patent Application Laid-Open Publication No. 186626/1985. More particularly, the conventional hot water circulating system is so constructed that hot water produced in a water boiler is forcibly fed to a radiator which takes a suitable form such as a fan coil unit, a floor mat or the like by means of a vapor or steam pressure to discharge heat at the radiator and then returned to the water boiler. Unfortunately, in the conventional hot water circulating system, when fresh water is supplied from an open tank to the water boiler after water is emptied out of the water boiler, the supplied water is caused to be immediately boiled to produce a large amount of steam in the water boiler, so that the pressure of the steam hinders the fresh water from being successively fed from the open tank to the water boiler. In order to eliminate such a disadvantage as described above, the assignee proposed a lot of hot water circulating systems, for example, as disclosed in Japanese Patent Publication No. 15492/1988.
Nevertheless, each of the proposed hot water circulating systems as well as the conventional system described above each is disadvantageous in that even when the timing of opening a valve to feed water from the open tank to the water boiler is deviated in only a small amount, a large amount of steam is caused to be produced in the water boiler as soon as water is supplied from the open tank to the water boiler, leading to an air lock phenomenon which interrupts the circulation of water through the system. For example, when a simple valve such as a check valve is used for this purpose, a small degree of variation in temperature at each section of the system, operating conditions or the like causes the circulating cycle to be suddenly interrupted during the operation of the system.
Also, the conventional hot water circulating system has another disadvantage that water escapes in the form of vapor from the open tank in use of the system because the temperature of the water is increased above an ambient temperature, so that it is required to frequently replenish the open tank with water.